The present invention relates to components of catalysts for the polymerization of olefins and the process for their preparation, the catalysts obtained from them and the use of the said catalysts in the polymerization of olefins. Homogeneous catalysts for the polymerization of olefins obtained from compounds of formula MLx in which M is a transition metal especially Ti, Zr, Hf, Cr, Pd and Ni, L is a ligand that is coordinated to the metal, and x is the valence of the metal, are known from the literature. Examples of catalysts of this type with very high activity are those obtained by reacting metallocene compounds Cp2ZrCl2 or Cp2TiCl2, or their derivatives substituted in the cyclopentadienyl ring, with polyalumoxane compounds containing the xe2x80x94(R)AlOxe2x80x94 repeating unit, in which R is preferably methyl (U.S. Pat. No. 4,542,199 and EP-A-129368). Catalysts of the aforementioned type in which the metallocene compound contains two indenyl or tetrahydroindenyl rings with a bridging bond to lower alkylenes or to other divalent radicals are suitable for the preparation of stereoregular polymers of propylene and of other alpha olefins (EP-A-185918).
Stereospecific catalysts are also obtained from dicyclopentadienyl compounds in which the two rings are substituted in various ways with groups with steric hindrance such as to impede the rotation of the rings about the axis with the metal. The substitution of the cyclopentadienyl ring of indenyl or tetrahydroindenyl in suitable positions supplies catalysts that are endowed with very high stereospecificity (EP-A-485823, EP-A-485820, EP-A-519237, U.S. Pat. No. 5,132,262 and U.S. Pat. No. 5,162,278). The catalysts described above supply polymers with very narrow molecular weight distribution (Mw/Mn of about 2).
Furthermore, some of these catalysts have the property of forming copolymers of ethylene with alpha olefins of the LLDPE type or elastomeric ethylene/propylene copolymers with very uniform distribution of the comonomenic units. The LLDPE polyethylene obtained is further characterized by low solubility in solvents such as xylene or n-decane.
The polypropylene obtained with the more stereospecific catalysts mentioned above exhibits greater crystallinity and a higher distortion temperature relative to the polymer obtainable with the conventional heterogeneous Ziegler-Natta catalysts.
Homogeneous catalysts with a different structure are described in international patent application WO 96/23010. These catalysts, comprising a complex between a transition metal and at least one bidentate ligand that has a particular structure, are capable of polymerizing olefins to give a wide range of polymers including copolymers comprising olefins and polar monomers such as carbon monoxide, vinylacetate, (meta)acrylates etc.
Despite their excellent properties in terms of quality of the polymeric products, considerable difficulties are encountered when said homogeneous catalysts are to be used in industrial processes of production of polyolefins that are not carried out in solution. The homogeneous catalysts in fact, are not able to provide polymers with a regular morphology when used in processes such as polymerization in gas-phase. In order to make it possible their use in non-solution polymerization processes, the homogeneous catalysts have to be made heterogeneous by supporting them on suitable supports that are able to endow the catalyst with appropriate morphological properties. Various kinds of supports can be used for this purpose including, among others, metal oxides such as silica, magnesium halides or polymeric supports such as polyethylene, polypropylene and polystyrene. A characteristic that is common to these supports is that they are porous and so enable the metallocene compound to be fixed by being deposited in the pores. The catalytic components thus obtained are therefore in the form of particles of inert material, organic or inorganic, carrying in the surface layer, in correspondence of the pores, the transition metal compound that constitutes one of the components of the catalyst. To achieve efficient support, however, the porosity of the support must be accurately controlled. Moreover, since the extent of supportation depends mainly on the porosity of the support particles, it also proves very difficult to achieve homogeneous distribution of the quantity of compound supported because the individual support particles or fractions have differences in porosity that are sometimes very considerable. In any case, the upper limit of the amount of transition metal compound that can be supported is always determined by the porosity of the support. For example, U.S. Pat. No. 5,106,804 describes catalysts comprising a metallocene compound supported on MgCl2 in spherical form and partially complexed with an electron-donor compound in which the amount of Zr compound supported on MgCl2 is relatively low (the Zr/Mg ratio in the catalyst is less than about 0.05). Furthermore, the polymerization yields are not such as to make it possible to obtain polymers containing sufficiently low residues of the catalyst. It is in fact known that supporting tends to lower the activity of homogeneous catalysts considerably. European patent EP 798315 describes a method of preparing homogeneous mixtures consisting of a metallocene, a cocatalyst and a dispersing medium having a oily or waxy consistency that is selected among the non-aromatic long-chain hydrocarbons that have boiling point above 150xc2x0 C. and viscosity of at least 1 Paxc2x7s at 25xc2x0 C. According to the inventors these mixtures are endowed with improved stability. Although included in the generic description, the use of a specific hydrocarbon matrix with a melting point above 70xc2x0 C. as a dispersing medium it is never described specifically. Nor, moreover, is there any specific description of a solid catalytic component in spherical form that comprises a homogeneous catalyst dispersed within a solid hydrocarbon matrix at room temperature. The only use of a solid dispersing medium is reported in Example 3 describing the preparation of solid mass of a paraffinic wax having a melting point between 65 and 70xc2x0 C. and containing methyl alumoxane in an amount equal to approx. 66 wt. %, which has then been mechanically comminuted to a fine grain powder. In addition to the fact that these mixtures do not possess a suitable morphology, it is also important to observe that according to Table 1 of the said application, the metallocene compound is not present in the formulation of Example 3. As it can be seen from the polymerization data, however, the yields that are obtained using this catalyst are very low even if further alumoxane is added in the reactor. International patent application WO 96/34020 describes a method of preparation of a solid catalyst that comprises supporting a metallocene and an activator on a support, preferably porous, and then coating the said supported catalyst with an inert organic material that is preferably a hydrocarbon component of molecular weight between 200 and 20 000 and is soluble in aromatic solvents at temperatures above 70xc2x0 C. According to the said patent application, the catalyst thus prepared makes it possible to overcome the problem of reactor fouling, but the polymerization yields (expressed in terms of kg of polymer per g of transition metal) are very low. Surprisingly, it was found that the solid components of catalysts obtained by dispersing a homogeneous catalyst within a hydrocarbon matrix possessing certain characteristics are capable of forming catalysts that have high activity and are able to produce polymers with excellent morphological properties. An object of the present invention therefore comprises spherical catalyst components for the polymerization of formula RCHxe2x95x90CHR, in which R is independently hydrogen or a hydrocarbon group with 1-10 carbon atoms, comprising a homogeneous transition metal compound of formula MPx, in which M is a transition metal from Groups 3 to 11 or the lanthanide or actinide Groups of the Periodic Table of the Elements (new IUPAC version), P is a ligand coordinated to the metal M and x is the valence of the metal M. The transition metal compound is dispersed in a solid hydrocarbon matrix that has a melting point above 70xc2x0 C. Hydrocarbon matrices with a melting point above 80xc2x0 C. are particularly preferred, and even more preferably above 90xc2x0 C. The said matrix is preferably selected from the group comprising solid paraffinic waxes, polyolefins or their mixtures. The use of solid paraffinic waxes is particularly preferred.
Preferably, moreover, the said matrix, in contrast to the supports commonly employed in this technology, is characterized by very low porosity. In particular the porosity, measured by the mercury method, is less than 0.3 cm3/g and preferably below 0.15 cm3/g. The solid paraffinic waxes are generally indicated as the products that are derived from the fraction of lubricating oils that is in its turn obtained by fractional distillation of crude oil. When this fraction is cooled the waxes separate from the oils and are deposited as solid products, which are then recovered by filtration. From the chemical standpoint, the waxes are mixtures comprising straight-chain, branched-chain or cyclic hydrocarbons. The polyolefins that can be used as solid matrix of the present invention comprise the polyolefins generally known in the art, such as (co)polymers of ethylene (HDPE, LLDPE), of propylene (isotactic, atactic and syndiotactic homopolymers of polypropylene, random copolymers with ethylene, butene-1, hexene-1 or their mixtures) and of butene as well as polyolefins obtained by the polymerization of vinylaromatic monomers such as styrene, divinylbenzene, etc. Among the polyolefins that can be used according to the present invention, the preferred ones are the (co)polymers of ethylene having low and very low molecular weight (i.e. those having an intrinsic viscosity lower than 5, preferably between 0.1 and 4, the ethylene copolymers that have a percentage by weight of comonomer greater than 10%, the highly modified copolymers of propylene and the elastomeric ethylene-xcex1-olefin copolymers, possibly containing minor proportions of diene or polyene. As is well known, these polymers can be obtained for example by polymerization of the starting olefins carried out in the presence of catalysts of the Ziegler-Natta type comprising the product of reaction between an organometallic compound and a transition metal compound preferably selected from Ti or V. As described previously, the catalyst components of the invention comprise a compound containing a transition metal M selected from the Groups 3 to 11 or the lanthanide or actinide groups of the Periodic Table of the Elements (new IUPAC version). In particular, in the said compound the transition metal is preferably selected among Ti, V, Zr, Hf, Sc, Cr, Fe, Co, Ni, and Pd. In one of the preferred embodiments, the said transition metal compound is selected among the compounds of formula (I)
QLlZMXlp xe2x80x83xe2x80x83(I) 
wherein Q is a substituted or unsubstituted cyclopentadienyl radical, which can have one or more condensed cycles and which can contain heteroatoms, such as indenyl, tetrahydroindenyl, fluorenyl, octahydrofluorenyl, tetrahydrofluorenyl, indolyl, thiopenthyl, dithiophenecyclopentadienyl; Z has the same meaning as Q or it can be xe2x95x90NR8, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94 or xe2x95x90PR8, wherein R8 is hydrogen or a C1-C20-alkyl, C3-C20-cycloalkyl, C2-C20-alkenyl, C6-C20-aryl, C7-C20-alkylaryl or C7-C20-aryalkyl radical which can contain a heteroatom; L is a divalent bridge connecting the moieties Q and Z preferably selected from the group consisting of C1-C20-alkylidene, C3-C20-cycloalkylidene, C2-C20-alkenylidene, C6-C20-arylidene, C7-C20-alkylarylidene or C7-C20-aryalkylidene radicals which can contain a heteroatom; more preferably L is selected from the group consisting of CR32, C2R34, SiR32, Si2R34 or CR32SiR32 wherein R3 is hydrogen or a C1-C20-alkyl, C3-C20-cycloalkyl, C2-C20-alkenyl, C6-C20-aryl, C7-C20-alkylaryl or C7-C20-aryalkyl radical which can contain a heteroatom; preferably R3 is hydrogen, methyl or phenyl; M is a transition metal M from Groups 3 to 10 or the lanthanide or actinide groups of the Periodic Table of the Elements (new IUPAC version); X is a ligand, same or different, selected from hydrogen, a halogen, or a R9, OR9, OSO2CF3, OCOR9, SR9, NR92 or PR92 group, wherein R9 is hydrogen or a C1-C20-alkyl, C3-C20-cycloalkyl, C2-C20-alkenyl, C6-C20-aryl, C7-C20-alkylaryl or C7-C20-arylalkyl radical, optionally containing a heteroatom; p is an integer of from 0 to 3, preferably from 1 to 3, more preferably 2, which integer is equal to the oxidation state of the metal M minus 2; and l is 0 or 1. Non-limiting examples of compounds of formula (I) are those described in WO 98/22486, WO 99/58539 WO 99/24446, U.S. Pat. No. 5,556,928, WO 96/22995 EP-485822 and EP-485820. Another class of preferred catalysts is that comprising a late transition metal complex corresponding to formula (II) or (III):
LMXpXxe2x80x2sxe2x80x83xe2x80x83(II) 
LMAxe2x80x83xe2x80x83(III) 
wherein M is a metal belonging to Groups 8, 9, 10 or 11 of the Periodic Table of the Elements (new IUPAC notation); L is a bidentate or tridentate ligand of formula (IV): 
wherein B is a C1-C50 bridging group linking E1 and E2, optionally containing one or more elements of Groups 13-17 of the Periodic Table; E1 and E2 are elements, the same or different from each other, belonging to Group 15 or 16 of the Periodic Table and are bonded to metal M; the substituents R1, the same or different from each other, are hydrogen or a linear or branched, saturated or unsaturated C1-C20 alkyl, C1-C20 alkylidene, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl and C7-C20 arylalkyl radical, optionally containing one or more elements of Groups 13-17 of the Periodic Table of the Elements, such as B, Al, Si, Ge, N, P, O, S, F and Cl atoms; or two R1 substituents are attached to the same atom E1 or E2 to form a saturated, unsaturated or aromatic C4-C8 ring, having from 4 to 20 carbon atoms; m and n are independently 0, 1 or 2, depending on the valence of E1 and E2, so as to satisfy the valence number of E1 and E2; q is the charge of the bidentate or tridentate ligand so that the oxidation state of MXpXxe2x80x2s or MA is satisfied, and the complex of formula (II) or (III) is overall neutral; X are monoanionic sigma ligands, the same or different from each other, selected from the group consisting of hydrogen, halogen, xe2x80x94R, xe2x80x94OR, xe2x80x94OSO2CF3, xe2x80x94OCOR, xe2x80x94SR, xe2x80x94NR2 and xe2x80x94PR2 groups, wherein R is a linear or branched, saturated or unsaturated C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl or C7-C20 arylalkyl radical, optionally containing one or more atoms belonging to Groups 13-17 of the Periodic Table of the Elements (new IUPAC notation), such as B, N, P, Al, Si, Ge, O, S and F atoms; or two X groups form a metallocycle ring containing from 3 to 20 carbon atoms; the substituents X are preferably the same; Xxe2x80x2 is a coordinating ligand selected from mono-olefins and neutral Lewis bases wherein the coordinating atom is N, P, O or S; p is an integer ranging from 0 to 3, so that the final complex of formula (II) or (III) is overall neutral; s ranges from 0 to 3; and A is a xcfx80-allyl or a xcfx80-benzyl group.
According to a preferred embodiment of the present invention, the bridging group B corresponds to a structural formula selected from the group consisting of: 
wherein G is an element belonging to Group 14 of the Periodic Table, and is preferably C, Si or Ge; r is an integer ranging from 1 to 5; E3 is an element belonging to Group 16 and E4 is an element belonging to Group 13 or 15 of the Periodic Table; the substituents R2, the same or different from each other, are selected from the group consisting of hydrogen, linear or branched, saturated or unsaturated C1-C20 alkyl, C1-C20 alkoxy, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl and C7-C20 arylalkyl radicals, optionally containing one or more atoms belonging to groups 13-17 of the Periodic Table (such as B, Al, Si, Ge, N, P, O, S, F and Cl atoms); or two R2 substituents form a saturated, unsaturated or aromatic C4-C8 ring, having from 4 to 20 carbon atoms, or they form a polycyclic ring system, optionally containing one or more Group 13-16 elements; a substituent R1 and a substituent R2 may form a substituted or unsubstituted, saturated, unsaturated or aromatic C4-C8 ring, having from 4 to 20 carbon atoms and optionally containing one or more Group 13-16 element.
In the bidentate or tridentate ligand L of formula (IV), El and E2 belong to Group 15 or 16 of the Periodic Table, and preferably are selected from the group consisting of N, P, O, and S.
In the late transition metal compounds of formula (II) or (III), the substituents R1, the same or different from each other, are preferably bulky groups; more preferably, they are C6-C20 aryl groups, and even more preferably are substituted in the 2 and 6 positions with a C1-C10 alkyl group. The substituents X are preferably hydrogen, methyl, phenyl, Cl, Br or I; p is preferably 1, 2 or 3. When Xxe2x80x2 is a neutral Lewis base wherein the coordinating atom is N, P, O or S, it is preferably selected from the group consisting of phosphines, amines, pyridines, nitriles, sulfides and ethers; even more preferably, it is selected from the group consisting of triphenylphosphine, tri(C1-C6 alkyl)phosphines, tricycloalkyl phosphines, diphenyl allyl phosphines, dialkyl phenyl phosphines, triphenoxyphosphine, pyridine, di(C1-C3 alkyl) ether, tetrahydrofuran and nitriles, especially acetonitrile.
When Xxe2x80x2 is a mono-olefin, it is a hydrocarbyl group having one carbonxe2x80x94carbon double bond, having from 2 to 20 carbon atoms; preferably a substituted or unsubstituted C2-C6 alkene. The variable s is preferably 0 or 1. A is xcfx80-allyl or a xcfx80-benzyl group.
By a xcfx80-allyl group is meant a monoanionic ligand with 3 adjacent sp2 carbon atoms bound to a metal center in an xcex73 fashion. The three sp2 carbon atoms may be substituted with other hydrocarbyl groups or functional groups. Typical xcfx80-allyl groups include: 
wherein R is hydrocarbyl.
By a xcfx80-benzyl group is meant xcfx80-allyl ligand in which two of the sp2 carbon atoms are part of an aromatic ring. Typical xcfx80-benzyl groups include: 
The quantity of transition metal compound present in the component of the present invention can vary over a wide range. Generally the quantity varies between 0.01 and 50 wt. % relative to the total weight of the component, preferably between 0.5 and 25% and more preferably between 1 and 10%. In particular, when the transition metal compound is selected from among the compounds of formula (I) its quantity is preferably between 1 and 6%. As already mentioned, the components of the invention form, with one or more compounds capable of activating the transition metal compound, catalysts that are particularly suitable for the polymerization of olefins. A class of activator compounds that are particularly preferred comprises organometallic compounds of aluminium. Particularly preferred are the alumoxanes and/or a compound able to form an alkylmetal cation. Suitable activating agents are linear alumoxanes having the formula: 
wherein the R17 substituents, the same or different from each other, are hydrogen or a linear or branched, saturated or unsaturated C1-C20-alkyl, C3-C20-cycloalkyl, C6-C20-aryl, C7-C20-alkylaryl and C7-C20-arylalkyl radical, optionally containing Si or Ge atoms; and t is an integer ranging from 0 to 40; or cyclic alumoxanes having the formula: 
wherein t is an integer ranging from 2 to 40 and R17 has the meaning above.
Examples of alumoxanes suitable as activating cocatalysts in the catalysts system according to the present invention are methylalumoxane (MAO), 2,4,4-trimethyl-pentylalumoxane (TIOAO), 2-methyl-pentylalumoxane and 2,3-dimenthyl-butylalumoxane. Mixtures of different alumoxanes can also be used. Activating cocatalysts suitable as component (B) in the catalysts of the invention are also the product of the reaction between water and an organometallic aluminum compound; particularly suitable are the organometallic aluminum compounds described in the European patent application EP 0 575 875 (formula (II)) and in the international patent applications WO 96/02580 (formula (II)), WO 99/21899 (formula (II)) and in the European patent application no. 99203110.4 (formula (II)). Non-limiting examples of organometallic aluminum compounds are:
tris(methyl)aluminum, tris(isobutyl)aluminum,
tris(2,4,4-trimethyl-pentyl)aluminum bis(isobutyl)aluminum hydride,
bis(2,4,4-trimethylpentyl)aluminum hydride isobutyl-bis(2,4,4-trimethyl-pentyl)aluminum
tris(2,3-dimethyl-hexyl)aluminum tris(2,3,3-trimethyl-butyl)aluminum
tris(2,3-dimethyl-butyl)aluminum tris(2,3-dimethyl-pentyl)aluminum
tris(2-methyl-3-ethyl-pentyl)aluminum tris(2-ethyl-3-methyl-butyl)aluminum
tris(2-ethyl-3-methyl-pentyl)aluminum tris(2-isopropyl-3-methyl-butyl)aluminum
tris(2,4-dimethyl-heptyl)aluminum tris(2-phenyl-propyl)aluminium
tris[2-(4-fluoro-phenyl)-propyl]aluminium tris[2-(4-chloro-phenyl)-propyl]aluminium
tris[2-(3-isopropyl-phenyl)-propyl]aluminium tris(2-phenyl-butyl)aluminium
tris(3-methyl-2-phenyl-butyl)aluminium tris(2-phenyl-pentyl)aluminium
tris[2-(pentafluorophenyl)-propyl]aluminium tris[2,2-diphenyl-ethyl]aluminium and
tris[2-phenyl-2-methyl-propyl]aluminium.
Mixtures of different organometallic aluminum compounds and/or alumoxanes can also be used. The molar ratio between aluminum and the metal M of the bridged metallocene compound is preferably comprised between 10:1 and 50,000:1, and more preferably between 100:1 and 4,000:1. Further alumoxanes suitable as activating agents in the process of the present invention are alkylhaloaluminoxanes, as described in the International Patent Application WO 00/22007, and in particular 1,3-dichloro-1,3-diethyldialuminoxane [EtAlCl]2O and 1,3-dichloro-1,3-diisobutylaluminoxane [iBuAlCl]2O. Other compounds capable of activating the transition metal compounds described previously are the compounds able to form an alkylmetallocene cation; preferably said compounds have formula Y+Zxe2x88x92, wherein Y+ is a Brxc3x8nsted acid, able to donate a proton and to react irreversibly with a substituent X of the metallocene compound of formula (I), and Z31  is a compatible non-coordinating coordinating anion, able to stabilize the active catalytic species which results from the reaction of the two compounds and which is sufficiently labile to be displaceable by an olefin substrate. Preferably, the anion Zxe2x88x92 consists of one or more boron atoms. More preferably, the anion Z31  is an anion of the formula BAr4(xe2x88x92), wherein the substituents Ar, the same or different from each other, are aryl radicals such as phenyl, pentafluorophenyl or bis(trifluoromethyl)phenyl. Tetrakis-pentafluorophenyl borate is particularly preferred. Other useful non-coordinating anions Zxe2x88x92 can be SbF6xe2x88x92, PF6xe2x88x92, BF4xe2x88x92, trifluoromethanesulphonate and p-toluenesulphonate. Moreover, neutral Lewis acids such as BAr3, SbF5 and BF3 can conveniently be used. The solid components according to the present invention can be prepared by a process comprising (a) dispersing a homogeneous transition metal compound according one or more of formulae (I)-(III) above, in a hydrocarbon matrix having a melting point above 70xc2x0 C. which has been brought in a liquid form and (b) solidifying the said matrix, containing the said transition metal compound, in the form of spherical particles.
According to a particular embodiment the transition metal compound is dispersed, with the aid of a mixer, in the molten hydrocarbon matrix and the mixture thus obtained is sprayed under temperature conditions such as to cause immediate solidification of the droplets as spherical particles. The conditions under which spraying and immediate cooling take place (flow rate and pressure of the carrier gas and its ratio to the quantity of mixture to be sprayed; flow rate, pressure and temperature of the cooling gas) can be properly selected according to the knowledge of the skilled in the art, in order to obtain average diameters of the solid particles over quite a wide range. In particular the solid particles that constitute the solid components of the present invention have a spherical morphology and dimensions between 1 and 400 xcexcm and preferably between 10 and 300 xcexcm. The term spherical morphology means, according to the present invention, particles possessing a ratio between maximum diameter and minimum diameter of less than 1.5 and preferably less than 1.3.
Before being dispersed in the matrix the transition metal compound is preferably dissolved with a minimum amount of solvent. For this purpose it is possible to use any inert hydrocarbon medium in which the transition metal compound is soluble, for example toluene, benzene and similar hydrocarbons. In particular, whenever possible, it is preferable to use a hydrocarbon solvent that has a boiling point below 120xc2x0 C. so as to facilitate its removal from the final product. The use of a low boiling solvent assisting both the dispersion of the transition metal compound and the availability of the hydrocarbon matrix in liquid form is particularly preferred when the transition metal compound can decompose at temperatures at which the hydrocarbon matrix melts in absence of solvent. In this case the concomitant use of a solvent which is able to at least partially solubilize the matrix can allow to lower the temperature at which the hydrocarbon matrix/solvent system becomes sufficiently and homogeneously liquid to permit the dispersion of the transition metal compound. In a particular aspect of the present invention, the solution of the said transition metal compound is brought into contact with the matrix in the solid state which is then melted, while stirring. In particular, excellent results have been obtained by dissolving, together with the transition metal compound, also the activator component for example AlEt2Cl (DEAC) or a polyalkyl-alumoxane of the type previously described, and in particular MAO or its mixtures with an Al-alkyl compound, using molar ratios of alkyl-Al compound/transition metal compound greater than 2, preferably between 5 and 500. The solutions that are obtained are in fact particularly suitable for providing components of catalysts that have high activity. An alternative method of preparation of the components of the invention comprises:
(i) feeding the hydrocarbon matrix and the transition metal compound, possibly precontacted with the activator compound, into an extruder;
(ii) extruding the said mixture in the form of filaments and
(iii) cutting the said filaments before they have solidified completely, obtaining discrete particles. The catalysts of the present invention have wide applications. In particular they can be used in all the olefin polymerization processes in which said transition metal compound catalysts are normally employed. For example, they can be used in the (co)polymerization of olefins of the type CH2xe2x95x90CHR or of the type RCHxe2x95x90CHR in which R is an hydrocarbon radical with 1-10 carbon atoms, of cyclic olefins and diene or polyene monomers. Furthermore, they can be used in the (co)polymerization of CH2xe2x95x90CHR olefins with polar monomers such as carbon monoxide, vinylacetate, maleic anhydride, halogenated olefins, for the preparation of modified polyolefins such as ethylene-vinylacetate (EVA) copolymers, copolymers of ethylene or propylene with maleic anhydride, or copolymers of ethylene and carbon monoxide (polyketones).
In particular the catalysts obtained from compounds of the type C2H4(Ind)2ZrCl2, C2H4(H4Ind)ZrCl2 and Me2Si(Me4Cp)2ZrCl2 are suitable for production of LLPDE (copolymers of ethylene containing smaller proportions, generally less than 20 mol. %, of C3-C12 alpha olefin) characterized by relatively low values of density relative to the content of alpha olefin, by reduced solubility in xylene at room temperature (less than approx. 10 wt. %) and by molecular weight distribution Mw/Mn between about 2.5 and 5.
The catalysts of the present invention can be used in the polymerization of olefins either carried out in the liquid phase, such as solution or suspension, or in gas-phase processes. In particular the use of the catalysts of the invention in the gas-phase processes is especially preferred as it makes it possible to obtain polymers that have good morphological properties. The said gas-phase process can be carried out working in one or more fluidized-bed or mechanically-stirred reactors. Polymerization is generally carried out at temperatures between 40 and 120xc2x0 C., preferably between 50 and 90xc2x0 C. When working in the gas phase, the working pressure is generally between 0.5 and 10 MPa, preferably between 1 and 2 MPa. Hydrogen or other compounds known in the art having the same function can be used as molecular weight regulators. Moreover, it is possible, prior to polymerization, to carry out a stage of pre-polymerization such as to make the said catalyst particularly suitable for the next polymerization stage. The pre-polymerization stage is particularly recommended whenever a solid hydrocarbon matrix is used that has a melting point below the temperature of the polymerization stage. In this case it is particularly preferred to carry out pre-polymerization at temperatures below the melting point of the hydrocarbon matrix with the aim of avoiding the loss of morphological properties owing to melting of the hydrocarbon matrix in the reactor. In this case the pre-polymerization is carried out in particular at temperatures between xe2x88x9210 and 70xc2x0 C. and preferably at temperatures between 0 and 50xc2x0 C. In general, the pre-polymerization can be carried out in the liquid phase, comprising an inert hydrocarbon solvent such as propane, hexane, heptane, isobutane or a monomer, or in the gas phase working at temperatures generally below 100xc2x0 C., preferably between 20 and 70xc2x0 C. As explained above, the pre-polymerization in gas-phase is especially preferred because it allows to preserve the morphology of the catalysts component. The pre-polymerization is carried out by polymerizing small amounts of monomer for the time necessary to obtain quantities of polymer between 0.5 g and 2000 g per g of solid component, preferably between 5 and 500 g per g of solid component and more preferably between 10 and 100 g per gram of solid component. Preferably, pre-polymerization is carried out with ethylene, propylene or their mixtures. The pre-polymerized catalyst thus obtained is then used in the next polymerization stage. The process for the polymerization of olefins according to the invention can be carried out in the liquid phase in the presence or absence of an inert hydrocarbon solvent, or in the gas phase. The hydrocarbon solvent can either be aromatic, such as toluene, or aliphatic, such as propane, hexane, heptane, isobutane or cyclohexane. The polymerization temperature is generally between xe2x88x92100xc2x0 C. and +100xc2x0 C., particularly between 10xc2x0 C. and +90xc2x0 C. The polymerization pressure is generally between 0.5 and 100 bar.
The following examples are given by way of illustration of the invention and are non-limiting. The properties indicated are determined according to the following methods:
The size of the catalyst particles is determined by a method based on the principle of the optical diffraction of monochromatic laser light with the xe2x80x9cMalvern Instr. 2600xe2x80x9d apparatus. The average size is given as P50.
The intrinsic viscosity is determined in tetraline at 135xc2x0 C.